Fuel metering system for gas turbine engines



Feb. 17, 953 w. L. DRAY ETAL 2,628,472

FUEL METERING SYSTEM FOR GAS TURBINE ENGINES I Filed Feb. 5, 1949 5sheets-sheet 1 A92 ERA if 'TTEJ.

Feb. 17, 1953 w. L. DRAY EI'AL FUEL METERING SYSTEM FOR GAS TURBINEENGINES 5 ,Sheets-Sheet 2 Filed Feb. 5, 1949 W. L. DRAY ETAL FUELMETERING SYSTEM FOR GAS TURBINE ENGINES Feb. 17, 1953 5 Sheets-Sheet 3Filed Feb. 3, 1949 INVENTORS 14 417554 0R4) W. L. DRAY EI'AL FUELMETERING SYSTEM FOR GAS TURBINE ENGINES Feb. 17, 1953 5 Sheets-Sheet 4Filed Feb. 5, 1949 Ill/Ill TORS A ;/7' Z Feb. 17, 1953 Filed Feb. 5,1949 w. L. DRAY ET AL 2,628,472

FUEL METERING SYSTEM FOR GAS TURBINE ENGINES 5 Sheets-Sheet 5 I 295zai-rzw gi 29 2: X326 3 4.. /.Z/ Z2 V "I.

26/ 3/5 E 3/9 a 3/2 3/6 3/2 3/7 3/0 fi 05051.5 rh'eow SW/TG'H 'IFTEEIPatented Feb. 17, 1953 UNITED STATES RA'E'EN'E OFFICE FUEL METERINGSYSTEM FOR GAS TURBINE ENGINES Delaware Application February 3, 1949,Serial No. 74,322

24 Claims. 1

This invention relates to a fuel feeding system for gas turbine engines,particularly turbojet and turbopropeller engines for aircraft; and anobject of the same is to reorganize and correlate a fuel control deviceof the type shown in the copending application of Frank C. Mock, SerialNo. 716,154, filed December 13, 1946 (common assignee) and a variablestroke injection pump, for example, a pump of the type shown in U. S.Patent No. 2,403,371, Ifield et al., to obtain fuel metering with theadvantages inherent in said control device and at the same time haveavailable the extremely high delivery pressures at the fuel dischargenozzles which are desirable for better atomization in engines havingcertain characteristics and which high pressures tend to produce boilingof the fuel when a by-pass relief system is used in maintaining thedesired pressure across the control.

Another object is to provide a fuel feeding system incorporating a fuelmetering device to which fuel is supplied under pressure by a variablestroke displacement pump wherein the pump stroke is advantageouslycontrolled as a function of the metering rate.

Another object is to provide a fuel feeding system of the type specifiedwherein the flow of fuel to the discharge nozzles will be highlysensitive to the action of a manual control such as a throttle valveover a relatively wide pressure range.

Another object is to provide a fuel feeding system for gas turbineengines having an inbuilt emergency control which is simple inconstruction, yet efiicient in operation, and which may be brought intooperation instantly and automatically whenever its use becomesnecessary.

A further object is to provide a fuel feeding s stern for gas turbineengines for aircraft incorporating an all-speed governor control formaintaining pilot selected engine speeds irrespective of changes in airdensity or aircraft speed and a variable displacement pump which isautomatically regulated to supply fuel under pressure to the controlwithout lag upon demand of the control.

A still further object is to improve the idling system in a control forgas turbine engines.

The foregoing and other objects and advantages will become apparent inview of the following description taken in conjunction with thedrawings, wherein:

Figure 1 is a view in elevation and partly broken away of a gas turbineengine for aircraft equipped with a fuel feeding system in accordancewith the present invention, said system being shown schematically;

Figure 2 is a view in longitudinal section of one of the variable strokedisplacement pumps;

Figures 3 and 4 are sectional schematic views of the fuel control deviceor unit generally indicated at '55 in Figure 1, Figure 3 showing thelower (input and pump control section) part, and Figure 4 the upper(regulator and governor section) part of said device;

Figure 5 is a plan view of the connection linkage between the mainthrottle or governor valve and the emergency throttle valve (note: thisview is taken from the layout or assembly drawing of the control asbuilt and is not schematic) Figure 6 is a wiring diagram of the electriccircuit for the emergency control;

Figures '7, 8 and 9 are curve charts illustrating the operation of theherein disclosed fuel feeding system; and

Figure 10 is a detail sectional view of a device or unit which coactswith the fuel head regulator valve to maintain a substantially constantidle flow at predetermined low engine speeds.

Referring first to Figure 1, a gas turbine power plant in the form of aturbojet propulsion engine for aircraft is generally indicated at l0 ingeneral, it comprises a compressor rotor assembly H, a turbine rotorassembly I2 and an exhaust unit including a tail cone l3.

The turbine rotor assembly includes a plurality of annularly disposedcombustion chambers l, each comprising an outer tubular shell in whichis mounted a flame tube or burner 15, spaced from the outer sheil andformed with a series of openings 56 for admitting compressed air intothe tube. An air adapter or header section, generally indicated at H, isdetachably connected to the front end of the burner assembly; itcomprises a plurality of air adapters ll, one for each combustionchamber, which direct air under pressure to said chambers, where itenters the flame tubes l5 and mixes with the fuel discharged from burnernozzles is to effect combustion, the expanded air and products ofcombustion being discharged from the burner tubes through stator bladesforming part of a nozzle diaphragm assembly i9 and then through theblades of a turbine rotor 28 to effect rotation of the latter.

The compressor rotor assembly mounts a dynamic compressor 2 I, which maybe either of the centrifugal of axial flow type, driven by the turbinerotor through suitable shafting, not shown, to force air under pressureinto the air adapters or headers ll.

The expanded air and products of combustion, after passing through theblades of the turbine 20, are discharged to the atmosphere through areaction tube 22 mounted in the exhaust cone [3, to effect propulsion ofan aircraft in which the engine may be mounted Propulsion may also beeffected, in whole or in part, by a propeller, not

shown, but which may also be driven from the turbine 20. v

The various accessories whichgo to make up the complete power plant IDare usually mounted at the front of the engine and in part housed by asuitable streamlined casing 23. Among these accessories is the fuelfeeding system of the present invention, which is removed from thehousing and shown schematically to simplify th drawings and description.

The fuel feeding system comprises in general a pair of variablestrokerdisplacement pumps 25, 25' operating to supply fuel underpressure in series to the fuel control unit or metering device 15.Although in the example shown two pumps are used, it will be understoodthat one or any number may be utilized, depending upon the requirementsof the particular engine to be supplied with fuel. v

Referring to Figure 2, the pump illustrated therein and generallyindicated at 25 is primarily of the type shown in U. S. Patent No.2,403,371. It comprises a suitable casing including a hollow body 26having therein a bearing section 21 and at its outer end a combinedbearing and end plate or cover 28. The section 2'! is formed with achamber, 29 in which is mounted a rotating plunger housing orbody 30having a drive shaft 3| projecting therefrom and provided at its outerend with a suitable drive spline 32 adapted to have a driving connectionwith the engine [9. The plunger housing 33 is formed with a series ofelongated bores 33 in each of which is mounted a plunger 3 3, the latterbeing positively urged in a fuel displacing or pumping stroke directionby means of a wobble plate 35 and in a fuel intake or suction strokedirection by a spring 36. The wobble plate is engaged within the innerrace 31 of a thrust bearing 38 and the entire wobble plate and bearingassembly is carried by a supporting member 39. Fuel from a suitablesource of supply fiows to the pumps by way of conduits 40 and 40' tointake port 4|; and when the springs '36 cause the plungers to exert asuction stroke,

the fuel is drawn into-the bores 33, and when said plungers are causedto exert a pumping stroke by the action. of the wobble plate, the fuelis discharged by way of port 42 and conduit 43 (or 43' from pump 25') tothe fuel line 44 (Figure 1) which leads to the fuel control or meteringdevice 15 shown more or less in detail in Figures 3 and 4. j

The stroke of the plungers is rendered variable by means of a springloaded piston 45 which is mounted to reciprocate in a chamber 45 and hassecured thereto a-rod 4'! which projects through a suitable guide bore48 formed in the housing 26 and connects by means of a link 49 with thewobble plate bearing support 39. The chamber 46 is open to'discharge-pressure at the one side.

(decrease stroke side) of the piston by way of a vent passage 56, and atthe opposite side (increase,

' the pump excess pressure and overspeed governor valve 51 or throughthe action of the pump control device or amplifier M5, to be described,the piston will be moved by discharge fuel pressure toa reduced outputposition.

A maximum pump pressure and overspeed governor assembly is provided andincludes a rocker arm 55 which is pivoted or fulcrumed at 53 and carriesvalve 5? at its one and adapted to control a'vent 5t forming acontinuation of a passage 58' leading tothe chamber t3 on the springside of the piston 45. A spring 59 normally urges the rocker arm 55 in adirection to cause the valve 5'! to close the vent 58; r The rocker armis rotated in a direction to open the vent passage 58 by the action of adiaphragm 6G,'Which separates chamber 8! from chamber'GZ, the chamber 6|being open to fuel inlet 'el ressure by way of passage 53 while thechamber 62 is open to inlet pressure by way of passage E i.

The diaphragm is is clamped between a pair of plates 65 and 65, theplate 65 having connected thereto a member 61- having a contact head 61adapted to engage the one'end of the rocker arm 55. A spring 88 connectsat one endto the member 57 and at its opposite endis connected to ananchor member 69, adjustable by means of a screw 79. V

When the pressure in chamber 35 on the stroke increasing side of piston45- (Which pressure is'a measure of pump discharge pressure) exceeds apredetermined value as set by the spring 59, it rocks the arm 55 in aclockwise direction, raising valve 51 and opening vent passage 58. Thisreduces the pressure in chamber 56 on the spring side of the pistons}?and the latter moves in direction to reduce the pump stroke.

The maximum speed governor function is obtained by meansof a centralbore 7! containin fuel at inlet pressure, and one-or more passages 12leading therefrom to the chamber 29-. When the speed of the rotatingplunger housing or body 30 exceeds a predetermined maximum, thecentrifugal action of the fuel thrown outwardly through the passage 72builds up pressure in the chamber 29 andthrough passage 64 in chamber 62to a point where the predetermined differential across the diaphragm fatis overcome and the latter is moved downwardly, 'opening'valve 51 andthe vent passage '58. I l I The fuel control device or unit is generallyindicated at 75 in Figure l. The lower part 15 of the unit includes thefuel input and pump control section of Figure 3 and it also includes theregulator valve assembly shown'at the bottom of Figure 4. a

Referring now to Figure 3, fuel under pump pressure flows to theinput-section by way of fuel line or conduit 44; it passes through afilter 78 located in a chamber 78'. The drop across the filter ispreferably held to a predetermined. maximum by a spring loaded reliefvalve!!! which controls a by-pass 8B, defined by a removable and.

see-ass 5. replaceable valve seat 86'. After passing through the filterT8, the fuel flows by way of passages 8| and 32, valve port 83, seeFigure 4, pass'age' 84, valve ports 85, 8B, passage 81, valve port 88and across a regulator valve 90' to regulator chamber 89 and governorchamber 89".

Valve port 83 is subject to closure by a normally open emergency controlsolenoid valve 260, Figure 3, and valve ports 85, 86 are controlled by aspring loaded pressure drop regulating valve I95, both of which valveswill be subsequently described.

From chamber 89", Figure l, the fuel flows across a governor valveIIII,.at whichpoint it is metered, the metered fuel then flowing to thefuel discharge nozzles I8 by way of annular chamber H15, valve chamberI61, chamber I59", conduit Illi (Compare Figure 4 with Figure 1),.across pressurizing valve andshut-off cock. IlI-,: through parallel lowand-high pressure conduits I88, I32 and ccacting fuel. manifolds W9,I93, and nozzle supply lines or pipes I190,- I'M".

The principal function of the regulator valve 90 is to maintain ametering head acrossthe governor valve as a function of engine" speed,so that irrespective of how suddenly or how much the governor valve maybe opened to accelerate the engine, the rate of fuel feed will notincrease beyond a certain value predicated on a maximum safe burnertemperature; and when the governor valve is closed to decelerate; themetering head will be such as to produce a gradual reduction in flow toprevent burner blowout or failure. The valve as shown in Figure 4consists of a hollow cylinderhaving, therein a plurality of holes ororifices 9 I adapted to register with the ports 88, whereupon fu'elflows through the interior of the cylinder to chamber 89; it is mountedto slide in a cylindricalhousing of bushing 92 secured in a; boss 93'formed integral with the main housing or casting; of the device.

A metering head diaphragm is indicated at 94; it is connected to thestem 95 ofthe regulator valve 99 through the medium of a ball head 95'formed on. the one endv of: said stem and. engaging m a: socket 9Bwhich: i'scarried by a diaphragm plate 91 coacting with an adjacentplate 98 to reinforce the central portion of the diaphragm 94, thelatter constituting a movable wall between unm'etered fuel chamber 89and a density compensating fuel chamber 99. A spring I bears at itsinner end against and is" centered by a dish-shaped portion formed inthe center of the diaphragm plate 98 This spring coactswith the unitshownin Figure t0' maintain the metering head at apredetermined'value atlow engine speeds, as Will be subsequently described.

A governor valve is indicated at IIII; it is in the form of a hollowcylinder formed with-a series of holes or ports I02 and is s'li'dinglymounted in a cylindrical valve cage'or sleeve I03 formed with entranceopenings or portsas'at I94; through which-"fuel from the chamber '89flows into-the valve cylinder and thencepasses through ports 102 andI'flBto annular valve chamber I065 The governor valve WI is-securedon anelongated valve stem or red It'l At its left-hand end, the stem- Iill'is abutted by a rod IBB' provided at its outer extremity with athreadedscrew'head I08 secured'ina bushing I09; the latter in turnbeingmounted in' th'emainhousing of thecontrol and secured in place b'y meansof an end'pla-te l I0; The'rod I fl8' ccnstitutes a minimum new setting"6.. means or stop" in' that it abuts the head it?" of the valve stem ID'f and determines the mini mum flow position of the governor valve IIlI.

A governor spring is indicated at III it abuts at its inner end the headIIl'l' of the valve stem I01 and at its outer end is engaged by abushing I I2 slidably mounted on" the rod I08, the bushin in turn beingengaged by the active end of a lever H3 adjustably secured on a shaftN4, the latter extending through the control housing and having securedon the outer end thereof a lever H5 (see Figures 1 and 5) which may becon-- trolled in any suitable manner from a remote point; in the presentinstance; to simplify the disc1osure;. it is connected to anadjustablelink is which in turn eohneets with the emergency throttle valve 210 andthrough the iatterwith the pilots control lever, as will be more fullydescribed.

The valve IilI is under the control of-an allspeed governor, including apair of governor weights, one of which is indicated at I H; it ispivotally mounted at H8 on al i-racket H 9 and at its" inner end isformed with an arm II? which bears against a, disc s'hape'd contact orbearing member I20 secured orrthe adjacent end of the stem (B1. Thebracket H9 is formedintegral with the inner end of a shaft- I2'2; whichis mounted in. bearings I23 and on its outer end carries a drivingspline" I24" adapted to be driven from the engine. A seal assembly, Igenerally indicated at I25, prevents the escape of fuel from the chamberas to the exterior'ofthe unit around the shaft 2 5. A slinger ring I26is formed on the inner end of a bearing hub or bushing I21- andfuiictionsto catch any fuel that may leak past the seal" 1,25 andthrowit outwardly-into a drain passage I28. I

An adjusting rod or screw I29 projects through and is threaded in thebushing I09; its inner end is adapted to engage the slidable bushing H2and determine the minimum governor spring loading and hence minimumengine speed when the pilot sets his throttle to its lowest idle"position and at which time lever H3 is clear of bushing H2. 7

The governor valve assembly as above described and as shown in Figure 4has certain important advantages. The basically essential elements ofthe all-speed governor arethe centrifugal or fly weights I H, which mustbe rotatably mounted, the governor or metering valve IIII and the springIII, the latter twoelements being nonrotatably mounted. These threeelementsbear a mutual operating relationship to one another. Thus Whenthe valve isat a given how position, the weights should be ata certainradius and the spring under a certain tension. Hence, it is desirableto-have a readily-adjustableyet secure association of these respectiveparts,- and this is afforded by the'assembly as herein disclosed. Bymeans or" the external adjustment provided by the end plate or collarIII], the sleeve I03 may be located or reset with respect to thegovernor valve Iii! to determinethe maximumeffective valve opening orarea at full throttle setting and secure mutual positioning of coactingparts forcalibration purposes; and this adjustment together with theminimum how and governor spring adjustments afforded by the screws orthreaded rods I08 and I29, which are both externally accessible,contribute materially to the ease and accuracy with which the fuel--control device may'b'e tested and serviced.

One of a pair of centrifugal head generating governor weights isindicated at I30; it is pivoted at I 3! on a bracket I32 projecting fromshaft I22 similar to bracket H9 and has the inner arm I30 thereofadapted to engage a sleeve I33 slidingly mounted on the cylindricalmember I03. A lever I34 is pivoted or fulcrumed at I35 and at its upperend is pivotally connected to the sleeve I33 at I35 and at its lower endis formed with a fork or yoke I31 which engages a sliding sleeve I38forming part of the constant head idle assembly of Figure 10. The sleeveI38 is slidably telescoped over a spring retainer or housing I39 inwhich a spring I40 is seated and at its freeend engages a flange I4Iformed on said sleeve. A nut I42 adjustably limits the travel of sleeveI38 under spring thrust. The free end of the retainer I39 is secured tothe stem of the valve 90.

At low engine speeds, as for example during starting, it is desirable tohave an idle flow which will give sufficient pressure at the dischargenozzles to obtain good atomization, and it isalso desirable that thisflow remain constant when the engine is operating below somepredetermined speed. This result is obtained by the device shown indetail in Figure 10. Thus, when the engine is above some predeterminedvalue, the force exerted by the centrifugal weights I30 holds the flangeI 4| of the sleeve I38 against the adjacent end of the retainermemberI39 and the spring has no eifect on the position of valve 90. How ever,at speeds belowsuch value, the spring force overcomes that of theweights and sleeve I39 moves clear of the member I39, whereupon saidspring acts to position the valve 90 and maintains the head across thethrottle valve IOI substantially constant. The spring I09 determines theminimum idle head regardless of speed. Thus, at altitude the idle speedmay be considerably above that set for the constant head idle device ofFigure 10, yet the fuel flow may still go so lean as to result in burnerfailure, or retard acceleration were it not for spring I00.

The maximum open position of the valve 90 is adjustably determined bymeans of screw I 43, accessible upon removal of a cap I44.

In the schematic view of Figure 4, one of the all-speed governor valveweights II"! and one of the centrifugal head generating weights 7 I30are shown arranged in what appears to be opposed relation, or 180 apart;In the control as actually built, however, there is a pair of all-speedgovernor weights and a pair of speed metering or centrifugal headgenerating weights pivotally mounted in opposed relation.

To compensate or correct the metering differential for changes in airdensity, an aneroid assembly generally indicated at I45 is provided andincludes a spring loaded bellows or capsule I45 which is anchored at oneend to a bushing I41 carried by an outer casing or housing, and at itsopposite or movable end is secured to an inverted cup-shaped member I48engaged with a connecting and guide rod I49 through an interiorrelatively light loading spring I50 acting counter to another heavierloading spring I50 located exteriorly of said member within the bellows.It is preferred to use a pair of coacting springs as shown to improvethe sensitivity of the aneroid. The bellows I46 is loaded for responseto changes in both pressure and temperature (see Patent 2,376,711 to F.C. Mock), and is preferably located where it willbe subjected to ram orcomv pressor inlet pressure. The rod I49 is pivotally connected to theone end of a lever I5I, the opposite end of said lever being secured tothe outer end of a shaft I52, rotatable in a sealed bearing I53supported by a housing I54. The one end of shaft I52 projects into achamber I55 and has secured thereon a lever I56, which is pivotally andadjustably connected to the lower end of a density compensating needlevalve I51, mounted for sliding movement in a bushing I58 and contouredat its upper end to regulate the flow of fuel through a variable orificeI59. A pair of density circuit control jets I60 communicates theunmetered fuel chamber 89 with the density compensating fuel chamber 99;and fuel may fiow from the chamber 99 to the orifice I59 by way ofpassage IBI, annular chamber I62 and ports I62. From the orifice I59,fuel may flow to chamber I63 and thence by way of drilled passage I54 tothe metered fuel chamber I09.

The fuel pressures existing in the various flow passages and chambersmay be appropriately designated as follows:

Pry-Pump discharge pressure P1Control inlet pressure P2Unmetered fuelpressure P3Density compensating pressure P4Metered fuel pressure Sincethe shaft I22, which carries the speed metering weights I30, is drivenin relation to engine speed, said weights will exert a force tending toopen the regulator valve 90 proportional to the square of engine speed.As this valve opens, however, P2 pressure builds up in chamber 89 andacts on the diaphragm 94 in a direction tending to close the valve. Thepressure differential across diaphragm 94 is imposed across the feedrestriction defined by the governor valve holes or ports I02 in relationto ports I05, and since this differential is proportional to th squareof engine speed, for any given position of the said governor valve andthe density needle I51, the velocity and hence the weight of fuelflowing through said restriction or across said valve will beproportional to the square root of this difierential or to the speeddirectly. Movement of the governor valve in a direction to increase thearea of the feed restriction (to the right in Figure 4) momentarilydecreases the differential across the diaphragm 94, whereupon theregulator valve 90 moves toward open position (also to the right), feedof fuel to the burners is increased and the engine speeds up until thegovernor weights II I balance the newsetting of the governor spring I IIand a condition of equilibrium is obtained; movement of said governorvalve in a direction to restrict the area of the feed restriction hasthe opposite effect. During acceleration and deceleration, therefore,the metering head will vary as a function of engine speed, as will alsothe quantity of air flowing to the burners.

Upon a decrease in the density or the air flowing to the engine, lessfuel is required to drive the turbine and. compressor at a given speed,and unless the maximum rate of fuel delivered to the engine onacceleration is correspondingly reduced, much higher burner temperatureswill be experienced during acceleration at altitude than at sea levelunder similar engine conditions, due to the extremely rich fuel-airratio. This is the reason for the density control circuit justdescribed. A decrease in entering air density causes elongation of thebellows I46 and an increase in the area of the orifice I59, while anincrease in density has the opposite effect.

For a given engine or turbine speed, the differential across themetering head diaphragm 94 (Pa-P3.) will be constant, and hence the flowthrough the control jets I58 at this time will be constant. All fiow offuel through jets I60 will pass through the orifice I59, and hence thedrop across the latter orifice will vary inversely as the square of itsarea, and for a fixed or given position of the needle I51 (constantdensity) the drop across the orifice I58 (Pa-P4) will be proportional tothe drop across the jets IIiIl (P2P3). The sum of the drop across theorifice I58 and the drop across the diaphragm 94, or jets I60, issubstantially equal to the drop across the governor valve IIlI (P2-P4),and. at a given density, the total drop will be proportional to thesquare of engine speed. As the effective area of orifice I59 isenlarged, there will be a corresponding decrease in the drop across thisorifice and a reduction in head across the governor valve IOI, resultingin a diminishing fi'ow of fuel to the burners for a given area of thefeed restriction defined by the governor valve orifices I82 and the(meeting ports I85. Thus, if the governor valve IIII is opened foracceleration at a certain altitude, less fuel will be supplied to theburners than would be the case at ground level or at some loweraltitude. By suitably contouring the needle I51, substantially completedensity compensation may be obtained. This advantage is not only presentupon acceleration and deceleration, but it also will maintain a givenengine or turbine speed at all altitudes for any fixed or given positionof the pilots control lever, or the governor valve I I 3'.

From annular chamber I06, Figure 4, metered fuel flow-s past one-wayflap valve I65, which is hinged at I66, into valve chamber I61 and outthrough ports I58 into chamber I59, thence by way of conduit I to thefuel shut-off and twostage nozzle pressure valve assembly or unitgenerally indicated at IN. This unit comprises a shut-off valve I12which at its lower end con- The valve I12 is hollow or is trols a portIla. formed with a passage I14 which when the valve is closedcommunicates with or is vented to the fuel input conduit 40 by way ofports I15, annular chamber I15 and passage or conduit I11.

In this manner, the pressure across the valve is balanced when the valveis closed so that the valve will not tend to move to open position dueto a build-up of pressure upstream thereof and may be easily controlled.The shut-off cock of valve I12 is slidable in a bushing or bearing I18by means of a pinion or rack gear I18 in mesh with a toothed rack I80,said gear being secured on a shaft I8! which projects through the mainvalve housing and has connected to the outer end thereof a lever, I82.The valve is limitedin its reciprocatory movement bya screw I83. A ventI84 permits any fuel which may leak past the valve or its bushing toescape to drain or back to the fuel tank, as desired.

The valve indicated at I85 is for use with a so-called duplex ortwo-stage spray nozzle; that is, a nozzle in which fuel at a lowmetering head flows through a set of primary pass-ages to a dischargejet, and when the metering pressure reaches a certain value, the fuel isautomati- I8 by way of passage I81, low pressure fuel line I88, manifoldring I89 and fuel lines I90 only. but when the metering head increasesbeyond a predetermined value, the valve I moves to open position andpermits fuel to flow to the said nozzles by way of valve chamber I9I,fuel line I92, main fuel manifold ring I93 and fuel lines I94.

Up to this point, the fuel control unit, with the exception of thetwo-stage nozzle and coacting valve and other structural changes indesign, is substantially the same as that disclosed in the copendingapplication of Frank 0. Mock, Serial No. 716,154, heretofore noted.

The valve indicated at I95, Figure 3, for controlling port 85 is anautomatic throttling valve; it tends to maintain a constant pressuredrop across the control, overcomes lag in P0 or pump discharge pressure,and it coacts with the pump stroke control device or amplifier Z'Ili tomaintain pump output pressure above a low unstable range. The valveitself is shown as of cylindrical form mounted to slide in a sealedbushing I 95 formed with a mounting flange I96, eetween which and aplate I91 is secured a diaphragm I88, the latter constituting a movablewall or partition between chambers I and 200. To insure properfunctioning of the diaphragm, chamber I59 is vented to chamber 200 byvent ZGI and passage 202. A spring 203 has its one end abutting astepped bushing 204 seated in a cap or cover 285, and its opposite endengaging a cup-shaped member 205 having a stem '2!" slidably projectingthrough an opening 208 in the bushing 284, movement of the member 205 ina valve opening direction being limited by adjustable nut 209. The valveI85 has connected thereto a stem 2 I 0 which projects through the centerof the diaphragm I98 and carries a coneshaped abutment member 2 whichprojects into the cup 206. Metered fuel or P4 pressure is communicatedfrom chamber I06 of Figure 4 to the valve opening side of the diaphragmI98 of Figure 3 by way of passage 2|2, annular chamber 2I3 and chamber200, the passage 2'I'2 having a calibrated bleed or restriction 2I'2'therein.

The effective exposed areas of the diaphragm I98 and valve I55 arepreferably such that the P1 pressure on opposite sides thereof balancesthe valve, and hence the P1 pressure in passage '81 will be maintainedat a constant value over and above metered fuel or P4 pressure asdetermined by the effective force of spring 203, or in other words,there will be a substantially constant pressure drop across theregulator valve 90 and governor or main throttle valve Ill-I. The valveI is also arranged to coact with a minimum pump output pressure deviceor amplifier generally indicated at '2I5 and which will now bedescribed.

The pump stroke control device or amplifier 2I5 comprises a rocker arm2I6 which is fulcrumed on a shaft 2 I1, journaled at its opposite endsin a housing 2H3 provided with a cap or cover 248. At its one end (upperend as -shi ulvn in Figure 3) the rocker arm carries a half ball valve2I8 adapted to control a vent passage 220, through which fuel from thespringside of the pump control piston '45 in control chamber 0'6, seeFigure 2, may by-fpa'ss back to the low pressure side of the pumps byway of 'passage22l, restriction 222, valve chamber 223, port 224,passage defined by conduits 225, 226, 2'26, see Figures 1 and 3, vent220, chamber 221, passage 228 and conduit 228'. The rocker arm ZIB isurged in a direction tending to unseat valve 2|! by P0 or pump dischargepressure which acts 11 en'- a small diaphragm 230 and through the latteron a piston 23! slidingly mounted in a cylinder 232 and at its outerfree end engaging an adjustable contact 233 carried by the said rockerarm 2|6. Pump discharge pressure is communicated to the diaphragm 236from passage or chamber 8% by way of passage 23 i, valve ports 235, 236,valve chamber 237 and passage 238. To dampen out any pressurefluctuations, an attenuator valve 239 is inserted in a valve bodyrelation; they act like a condenser in that surges in pressure aredampened out as the fuel encounters resistance to sudden changes inflow.

The rocker arm ZIS is urged in a direction tending to seat valve 2 H! bymetered fuel or discharge pressure (P4) which acts on a small diaphragm245 and through the latter on a piston 24% slidingly mounted in acylinder 22! and at its outer free end engaging an adjustable contact248 carried by said arm. Metered fuel pressure is communicated to thediaphragm 245 from annular chamber H96 of Figure 4 by way of passage245; and this pressure is assisted by a spring 258 inserted between apair of contact plates 25! and 252 and adjustable by a screw 253.

The so-called amplifier or pump stroke control device just describedoperates as follows:

Upon an increase in metered fuel or P4 pressure, due to an openingmovement of the main throttle or governor valve 15! or an increase inthe metering head across said valve, the piston 245 acts on the lever2l5 in a direction tending to hold the valve 2|9 seated. This restrictsor prevents escape of fuel from the spring side of the piston 45 inchamber 48 of the pump 25 (also the pump 25"), and hence the. piston 55will be urged in a direction for maximum pump output at a given speed.Also, an increase in P4 pressure causes the valve I95 to be urgedtowards open position to accommodate the demand for an increased supplyto the burners. The spring 250 of the amplifier 2|5 may be adjusted tobalance the amplifier in a manner such that at low or idle settings ofthe governor valve illl, a minimum pump output pressure may bemaintained, for example 500 p. s. i. Thus, should the valve IEH be movedto an idling position, which we can assume is the position of the partsshown .in Figure 4, then the valve I95 will move towards closedposition, and at a given engine speed the P pressure in chamber orpassage 84 will rise and act through the passage 238 on the piston 23ito move the rocker arm 2H5 in a direction to un seat the valve 2|9,thereby opening the vent 220 and permitting fuel to escape from thespring .side of piston 45 in pump control chamber 45, whereupon thepiston 35 moves to the left, or in a direction to reduceithe pumpstroke, but such reduction will cease when the spring force (spring 250)is balanced and the pump supply pressure will then remain substantiallyconstant until a further change in metered fuel or P4 pressure. Bycoordinating the setting of the valve I95 with that of the amplifier255, the

.pump output or Po pressure may be maintained above the low unstablepressure range at low throttle settings.

The bleed indicated at "54 is for bleeding off -a certain amount of P2or control pressure to a lower pressure source. As shown, the bleed isin "12 gives lo'w minimum flows, while at the same time, the clearancebetween valve and its sleeve or bushing 52 may be made large enough toinsure against sticking due to foreign particles or other matter in thefuel.

The small orifice indicated at 255 in Figure 4 is an altitude idle let;it is located upstream of the regulator valve and controls flow of fuelthrough a by-pass passage 255 from passage or chamber 87 direct tochamber 89'. The jet 255 is variable by means of a needle valve 257mounted in a sealed valve body 258 and adjustable by means of a screw25?. As heretofore noted in conjunction with the operation of thedensity control circuit, the metering head across the governor valve IOIis compensated for in manner such that as the air density decreases, duefor example to a gain in altitude, the'metering head is decreased tocorrespondingly decrease the flow of fuel to the burners. This, ofcourse, acts across the governor or main throttle valve It! at allsettings of the latter, hence the adjustable minimum flow stop I08 isprovided to prevent the engine speed from being reduced at altitude idlesettings to a point where the burners are in danger of failure from lackof fuel or compressor or turbine deficiencies make accelerationdifficult. Actually, the idle flow should be gauged by the ability ofthe spray nozzles to deliver a fairly well atomized spray. The needle25'! is preferably adjusted to give an effective area to' the jet 255which is less than the effective flow area of the metering restrictionsor orifices :02 when the governor valve 10! is up against its stop 508.Then, starting at sea level, the idle flow is determined by the minimumsetting of the governor valve and the head thereacross' as determined bythe density control circuit. As altitude is gained, however, the idleflow diminishes, since its quantity is affected by the area of thegovernor valve meterin restrictions I02 and the head across the valve,and the idle area remains fixed; also, the regulator valve 90 at idlespeeds comes up against the idle spring I00 or is governed by theconstant head idle spring I 45' and the head produced by the regulatorthen remains substantially constant. The jet 255 then determines theminimum idle flow (plus leakage across the density control circuit) andthe fact that this minimum is uncompensated for is of advantage inengines where the efliciency of the compressor lowers at high altitudes,since as altitude is gained, the idle speed increases and reduces thetendency to compressor or engines stall. Also, an increasedidle speed isdesirable at extremely high altitudes, since it becomes increasinglydifficult to accelerate as the idle speed decreases.

The emergency system comprises a normally open solenoid valve 260,Figure 3, which controls the port 83 just downstream of the filter l3said valve being connected to an armature ZEI which is moved in. avalveclosing direction upon energization of a coil 252. When the valve 258 isclosed. the fuel entering through conduit id is caused to flow by way ofa passage 253, valve port 255 and passage 255 to an emergency throttlevalve 225. The valve port 264 is controlled by a normally closedsolenoid valve 256 connected to an armature 267 which is moved in avalve opening direccuit in a manner such that when a condition arisesindicative of the necessity for emergency operation, the switchover fromnormal to emer- 13 gency operation occurs automatically, as will bedescribed in connection with Figure 6.

The emergency throttle valve 210 controls an orifice or restriction 21I; it is mounted to slide in a valve body 272 provided with a flangedcap screw 213. A spring 21% tends to stabilize the valve action. Atoothed rack 213 is connected to the one end of the valve 21.3 and ismounted to slide in the valve body 272 which is open or recessed at thispoint. The rack 2'53 is engaged by a gear or pinion 273 secured on ashaft 217, which projects outwardly through the housing 223 and isprovided with a lever 2'42, see Figure l, operatively connected to thepilots control lever in a manner to be described.

When the emergency system is in operation, fuel flows across theemergency throttle valve 2% and through conduit 2% to valve chamber 28!,see Figure 4, thence across one-way hinged flap valve 232 to chamberI51. From the latter chamber the fuel flows to the discharge nozzles H3in the same manner as does the metered fuel from the main control. Itshould be noted that when emergency fuel is flowing, the pressure inchamber 37 acts on the flap valve 155 to close the latter. This preventsthe emergency fuel from backing into the main control unit.

The emergency throttle valve till is preferably balanced to provide easein operation; it is formed with a central bore or passage res, seeFigure 3, through which fuel may pass and equalize the pressure acrossthe valve.

An emergency idle system is provided and consists of a needle valve 285which controls a variable jet 283, permitting a limited amount of fuelto flow across the emergency throttle valve 273 and from chamber Eelthrough passage 238, jet 233 and passage 233 to the conduit 238.

The pumps 25, 25 may be selectively isolated from one another and alsoheld in maximum stroke position at the will of a pilot or operator bymeans of a pair of isolating solenoid valves generally indicated at 2stand 2%, see Figures 1 and 2, which are of similar construction, eachcomprising a closure member or valve proper 29 l adapted to close therestricted orifice 222 and normally urged toward open position by aspring 292. The valve closure member is centrally abutted by a pin 23%secured to an armature 29 3. The solenoid coils for the two solenoidsare indicated at 255 and 293 and their coacting armatures at 2%, 296 tomore readily identify these parts in the diagram of Figure 6.

Check valves 2%, one of which is visible in Figure 2, in the pumpdischarge conduits 43, 43' prevent iuel under pressure from backing upthrough the pumps into the pump inlet in the event of failure of one ofthe pumps while the other is in operation.

Figure 5 shows the coordinating and connecting linkage between the mainthrottle or governor valve I ill and the emergency throttle valve 275The link H6 forming part of the main throttle or governor valve linkagepivotally connects at 333 with the one arm of a lever 30! which isadjustably secured on the shaft 211 for operating the emergency throttlevalve gear 216 of Figure 3. Also secured on shaft 21"! is an arm 382which at its outer free end is connected to a link 393, the latter beingconnected to the pilots main control lever (not shown). A maximum speedcontact 393 is adjustably secured on another arm of lever 39!. Thelinkage is shown in idle position. If a pull is exerted on arm 332through link 333, the main throttle arm H5 will r or unit 75.

be rotated counterclockwise, producing a similar movement to lever H3(Figure 4), thereby compressing the governor spring I I l and openingthe governor valve Ifll, at the same time resetting the overnor weightsIll; also the emergency throttle valve 210 is moved with the mainthrottle or governor valve to control the emergency metering orifice 2Hirrespective of whether or not the emergency system is in operation.

Figure .6 shows the electrical circuit for the emergency system and pumpisolating solenoids. A double pole, double throw'switch 3H] is locatedin the cockpit and. is adapted to be moved from the neutral positionshown into engagement with take-01f contacts 3H, 3H or emergencycontacts 3 l2, 3 [2. When the switch is engaged with contacts 3! l, 3|I, current may flow from a battery M3 or other suitable source of supplyto the pump isolating solenoids 295, 295 by way of line wire 3M, closingthe valves 222 of Figure 2 and permitting the springs 52 to move thewobble plates 35 to full stroke position. The circuit comprising thecontact 3H, wire EH5, contacts 3H5, .3l6', wire 313' and contact 3E2 isnormally open and is closed or energized automatically upon theoccurrence of some condition indicating loss of power; in the presentinstance it is closed whenthe nozzle (P4) pressure drops below apredetermined value by apressure switch assembly generally indicated at311 in Figures 1 and a and comprising a switch 3H, Figure 6, which iscarried by a spring loaded piston 318 mounted in a chamber 3 l9 ventedto P4 or nozzle pressure by conduit 323, the latter in Figures 1 and 4being shown as extending through a switch-supporting member 323'. Whenswitch 3|? closes, and assuming switch 310 to be in take-oil position,current flows through wires 3H5, 3I5, 32! to the coil 258 of thenormally closed solenoid valve 236 (compare Figure 6 with Figure 3)-opening this valve, and thence through wire 322, switch 323 and wire 324to the coil 262 or the normally open solenoid valve 233, closing saidlatter valve. Current also flows along wire 325 to a signal light 326,which indicates to a pilot that the emergency system is in operation.Unless the nozzle pressure drops below a predetermined value whileswitch 31a is in take-off position, only the pump isolating solenoidswill be energized. After take-oil", the pilot moves switch 3H3 to aneutral position, the pump solenoids are de-energized, and pump strokecontrol is automatic through the amplifier 215 which responds to thedrop across the metering device However, the pilot may go into emergencyat will simply by moving switch am into engagement with contacts 3|2, 3l2. A normally open lock-in relay switch 32! is provided and has a coil328 which is energized when the emergency circuit is energized andcloses the switch 321. This prevents the pressure switch 3!! fromcutting out the emergency solenoids when on emergency metering. Thepurpose of the switch shown at 323 is to facilitate a ground check ofthe emergency system.

Operation No starting mechanism has been shown since suitable type ofsuch apparatus may be used. Conventional starting systems usually employan electrical starting motor, controllable from the pilots compartment,for turning the engine during the starting period, and an ignitioncircuit including a spark plug or pilot flame located at one or more ofthe burners for igniting the'starting fuel.

When the engine is rotated, the pumps 25, 25' pressurize fuel in conduit44. Usually during starting, the governor or main thottle valve MI is inidle position, the position shown in Figure 4, and also at this time theconstant drop valve I95 and the regulator valve 99 Will be slightlycracked so that fuel may flow across these valves and also across thegovernor valve IUI to the metered fuel chamber I66 and thence to theburner nozzles I8 by way of chambers I61, I69, conduits I19 and I92 andfuel manifolds I89 and 193. Wh'en the engine reaches a self-sustainingspeed, the starting motor is disengaged.

' The pumps 25, 25 are preferably calibrated to deliver the maximumamount of fuel demanded by the control at any given engine speed withoutrequiring the pump plungers to go to full stroke position, so that athigh metered fuel or P4 pressures, there will still remain a certainrange of control through the amplifier 2I5.

Should the pilot move his control lever from idle to some higher or fullpower position, the lever II3 of Figure 4 will be turned to the right orcounterclockwise and compress the governor spring III, opening thegovernor valve WI and at the same time resetting the governor weightsII1, whereupon there is an increase in the flow of fuel to the dischargenozzles I8 (P4 pressure) and an increase in engine speed. Since thepumps 25, 25' Will'be driven at an increased speed, their output (Popressure) will be increased for a given position of the wobble plates.

Referring to Figure 7, the curve indicated at 330 represents the fuelfeed (pounds per hour) required for steady speed, that is, the rate atwhich fuel is fed to operate the engine at some predetermined speed at agiven entering air density. It can be assumed that Figure 9 is foroperation at sea level or a low altitude. The curve at 33I representsthe maximum rate of fuel feed or fuel-air ratio for safe burnertemperatures, say 1500 F.; while the curve at 332 rep-resents theminimum rate of fuel feed at a given engine speed for decelerationWithout danger of burner failure. Let it be assumed that the engine isoperating at speed 333 and the pilot opens governor valve IB-I to aposition which will produce speed 334; then the fuel supply duringacceleration will follow the arrows 335. The initial increase in flowrepresented by the vertical arrows occurs as a result of the increase inthe 'efiective area of the feed restrictions I02 at the then existingspeed. Should the pilot close the main throttle or governor valve IilIto decelerate, the fuel flow will follow the arrows 336.

When the area of the metering restrictions I 02 is increased by openingthe throttle valve, the differential across the regulator valvediaphragm 2t decreases, whereupon the regulator valve 38 moves towardsopen position, feed of fuel to the burners increases, and the enginespeeds up until the governor weights 1 balance the setting of thegovernor spring III and an equilibrium condition is obtained. Duringacceleration and deceleration, the metering head or differential acrossthe governor valve IOI and hence the rate of fuel feed will increase ordecrease as a function of engine speed and hence will be automaticallyheld within the predetermined upper or lower limits indicated by thecurves 33I and 332.

The curve chart of Figure 8 plots the P0 to P4 drop (Delta P) againstmetered fuel or P4 pressure. Note that as the metered fuel or nozzlepressure increases, the drop from P0 to P4 decreases while the dropacross the regulator and governor valves, P1 to P remains constant.Thus, as the governor valve HII is opened and the control demands morefuel, the valve 2I9 of the amplifier 255 will be held closed and thepump control pistons 55 will move in a direction to increase the pumpoutput at any given engine speed. Should the P0 or pump dischargepressure at any time exceed the requirements, the rocker arm 2 I 8 willbe rotated in a =counterclockwise direction, valve 2I9 will open andvent the spring side of each piston '45, and the pump output will beless at the then existing engine speed,

On take-off, the pumps are put in maximum stroke position to insure anample supply of fuel to the control unit; also, the emergency system isready for automatic switchover from metering on the main or primarycontrol. Thus, when the switch 3H) is :moved to a take-01f position, thepump isolating solenoids 295 and 295 are energized, and at the sametime, the emergency circuit is made ready so that should the nozzlepressure drop below a predetermined value, the pressure switch 3I1 ofFigure 6 will close. When this happens, the emergency control solenoids2i2 and 268 are energized, thereby closing the solenoid valve 266 andopening the solenoid valve 265. Since the emergency throttle valve 211iis linked to the main throttle or governor valve I0 I, the pilot has asingle control lever for both the main system and the emergency system.After take-off, the pilot moves the switch 3 It to a neutral position,and from then on the main control takes over.

Figure 9 illustrates how when operating on the emergency system the rateof fuel feed is varied in relation to movement of the pilots controllever. In this instance, the control of fuel feed, indicated by thecurve 331, becomes simply a matter of variation in the area of theemergency throttle restriction or orifice 21!. There is no compensationfor changes in entering air density, although each pump is protectedagainst excessive pressure build-up by the valve 51.

Although only one embodiment of the invention has been illustrated anddescribed, various changes in the form and relative arrangement of thepar-ts may be made to suit requirements.

We claim:

1. In a fuel metering system for an engine, in combination, a fuelcontrol device having a variable metering restriction and a throttlevalve for varying the area of said restriction, a regulator valve forcontrolling the metering head across said restriction, means forpositioning said regulator valve as a function of engine speed, anengine driven variable stroke displacement pump for ,pressurizin fuel tosaid control device having a pump control element movable to differentpos1tions to vary the pump stroke at a given engine speed, a valvelocated upstream of said regulator valv and adapted to maintain asubstantially constant pressure drop across said regulator valve andthrottle valve, said pump control element being responsive to thedifferential between the pressure upstream of said constant pressuredrop valve and metered fuel pressure.

2. In a fuel metering system for an engine, in combination, a fuelcontrol device having a fuel supply conduit provided with a meteringrestriction, a throttle valve for varying the area of said restriction,means for maintaining a substantially constant pressure drop across saiddevice; an. engine driven. variable stroke displacementpump forpressuri'zing fuel to said device having a control element movable todifferent positions to. vary the output of the pump at a given pump.speed, means for automatically controlling said element in accordancewith the demands of. the control device, said means operating tomaintain the pump output pressurev above a predetermined value at lowmetering settings of. the throttle valve.

3. In a fuel supply system for a gas turbine en gine, a. fuel controldevice having a fuel supply conduit provided with a metering restrictionand a throttle valve. for varying the area of said restriction, aregulator valve for controlling the metering head across saidrestriction, means for positioning said regulator valve as a function ofengine speed, a constant pressure drop valve for maintaining asubstantially constant drop across said regulator valve and throttlevalve; an engine driven variable stroke displacement pump forpressurizing fuel to said device having a pressure responsive controlelement movable to different positions to vary the output of the pump ata given pump speed; and means for subjecting said element to fuelpressures varying as a function of the drop across the control device,said latter means comprising a pressure regulating valve, a membercontrolling said valve, and means" for subjecting said member to thedifferential between the pressure upstream of said constant pressurevalve and metered fuel pressure.

4. A fuel supply system as clamed in claim 3 wherein said member isadjustable to maintain the pump output pressure above a low unstablevalue at low metering pressures.

5. In a fuel metering system for an engine, a main throttle valve, anemergency throttle valve, means operatively interconnecting said valvesfor synchronous fuel metering movement, and means for selectivelydirecting the fuel at will either to the main throttle valve or to theemergency throttle valve.

6. In a fuel metering system for an engine, a fuel control devicecomprising a main throttle valve, an emergency throttle valve, meansoperatively connecting said valves to a common control member, a fuelconduit for conducting fuel to said control device, means forpressurizing fuel in said conduit, means for diverting the flow of fuelto said emergency valve in the event of failure of the main control, andmeans responsive to a condition indicative of such failure forautomatically controlling said diverting means.

'7. In a fuel metering system for an engine, a main fuel control devicehaving a main throttle valve and an emergency throttle valve, meansoperatively connecting said valves to a common control member, a fuelconduit for conducting fuel to said device, said conduit having a branchfor conducting fuel to said emergency throttle valve, and a pair ofchange-over valves controllable to cut off the flow of fuel to said mainthrottle valve and direct the fuel to said emergency throttle valve inthe event of failure of said main control.

8. A fuel control device as claimed in claim 7 wherein the said flowcontrolling valves are of the electric solenoid type and are operativelyinterconnected by an electric circuit having- ''therein a pressureswitch responsive to a pressure condition indicative of the need foremergency 75 operation.

9. A fuel metering system as claimed in claim 7' wherein meansresponsive to changes in pressure of the metered fuel is arranged toautomatically" control said change-over valves;

10'. In a fuelmetering system for an aircraft engine, a fuel controldevice, said device being provided with a main throttle valve for normalfuel metering control and an emergency system including an emergencythrottle valve for control of metering when the emergency system is inoperation, means for supplying fuel: under pressure to said deviceincluding a fuelconduit having a metering restriction controlled by saidmainthrottle valve and a branch passage having a metering restrictioncontrolled by said emergency throttle valve, a pair of electric solenoidchange-over valves and an electric circuit therefor which whenenergizedcauses the latter valves to assume positions such as to closeoff flow" of fuel to the main throttle valve and di-rect"the fuel to theemergency throttle valve, said means for supplying fuel under pressureincluding a pair of variable stroke displacement pumps arranged tooperate in parallel and each having a pump control element normallybiased to maximum stroke position, means for communicating hydraulicoperating pressure to said control elements to actuate the latter as afunction of metered fuel flow, apair of pump isolating solenoid valvesin said circuit arranged to coact with said control elements in a.manner such that when the circuit is enegized, the valves close offhydraulic operating pressure to the control elements and permit thebiasing means to move the control elements toward maximum strokeposition, and a pilots control switch in said circuit movable totake-off position, emergency position and normal flight position, saidswitch when in take-off position causing operation of the isolatingvalves and when in emergency position causing operation of thechange-over valves and the isolating valves.

11. A fuel metering system as claimed in'claim 10 wherein said throttlevalves are operatively interconnected for control by a common controlmember.

12. A fuel metering system as claimed in claim 10 wherein there is apressure switch in said electric circuit responsive to a conditionindicative of the necessity for emergency operation, the arrangementbeing such that when the pilots switch is in take-off position and saidpressure switch is actuated, said change-over valves are also actuatedto direct the flow of fuel to the emergency throttle valve.

13. In a fuel metering system for aircraft gas turbine engines, a fuelcontrol device having a fuel conduit provided with a meteringrestriction and a throttle valve for varying the area of saidrestriction, a regulator valve for controlling the metering head acrosssaid restriction at a given position of the throttle valve, means forautomatically controlling said regulator valve as a function of enginespeed, means for automatically compensating the metering head forchanges in density of the air flowing to the engine. low or idling speedlimit means for said throttle valve for determining the minimum idlesetting of said throttle valve, and an altitude idle jet arranged toby-pass fuel around said regulator valve and provide a predeterminedamount of uncompensated idle flow across said throttle valve at highaltitudes.

14. In a fuel metering system for aircraft gas turbine engines, a fuelcontrol devicehavin'g a.

fuel conduit provided with a metering restriction, a throttle valve forvarying the area of said restriction, a low or idle speed stop for saidthrottle valve, means responsive to changes in entering air density forreducing the metering head across said restriction as density decreasesas by an increase in altitude, and an altitude idle jet in series withsaid metering restrict on and of less, elfective flow area than the areaof the 1 metering restriction when the throttle valve is up against itsidle'stop, the flow through said idle jet being uncompensated forchances in air density so that at extremely high altitudes the minimumidle flow remains constant.

15. In a system for supplying fuel under pressure to an engine, a valvefor regulating fuel flow, means responsive to changes in engine speedfor controlling said valve including a member for actuating the valve,and means for main taining a minimum substantially constant fueldelivery pressure irrespective of engine speed when the latter is belowa predetermined value comprising a second member movable with saidvalve, said second member providing an operating connection between saidactuating member'and valve when the latter is moved in an openingdirection, resilient means tending to separate said members with a forceof such magnitude as to effect separation only at engine speeds belowsuch predetermined value and maintain the fuel flow substantiallyconstant.

16. In a system for supplying fuel under pressure to an engine, a valvefor regulating fuel flow, means responsive to changes in engine speedfor controlling said valve including a member for actuating the valve,and means for maintaining a minimum substantially constant fuel deliverypressure irrespective of engine speed when the latter is below apredetermined value comprising a second member movable with said valveand providing an operating connection between said actuating member andvalve when the latter is moved in an opening direction, and asubstantially constant rate spring interposed between said members andtending to separate the latter with a force of such magnitude as toeffect separation only at engine speeds below such predetermined value.

17. In a system as claimed in claim 16 wherein said spring is seatedbetween a pair of telescopin members one of which constitutes saidsecond member and is secured to a projecting portion or stem of saidvalve and the other of which is slidable on said projection or stem andis contacted by said valve actuating member.

18., In a system for supplying fuel under pressure to an engine, athrottle valve, a valve for regulating the fuel head across saidthrottle valve, means for controlling said regulating valve as afunction of engine speed, and means for automatically maintaining theregulating valve in a position to establish a substantially constantmetering head when the engine speed is below a predetermined value.

19. In a fuel metering system for an engine, in combination, a fuelcontrol device having a variable metering restriction and a throttlevalve arranged to vary the area of said restriction to accelerate anddecelerate the engine, a regulator valve for controlling the meteringhead across stroke displacement pump for pressurizing' fuel to saidcontrol device having a pump control element movable to differentpositions tovary effective pump stroke at a given pump speed, and meansresponsive to the pressure drop across said; control device forautomatically positioning said element.

20. In a fuel metering system for an engine,im combination, a fuelcontrol device having a Val'i able metering restriction and a throttlevalve arranged to vary the area of said restriction to accelerate anddecelerate the engine, a regulator valve for controlling the meteringhead across said restriction, means responsive to an operating conditionof the engine for controlling said regulator valve, a constant pressuredrop throttling valve arranged tto maintain a substantially con stantpressure drop across said regulator valve and said throttle valve, anengine driven variable stroke displacement pump forp'ressurizing fuel tothe control device and having a pump control ele-* ment movable todifferent positions to vary the effective pump stroke at a given pumpspeed, and means responsive to the pressure diiferential between thepressure of the fuel upstream of said constant pressure drop valve andmetered fuel pressure for automatically positioning said element.

21. In a fuel metering device for an engine, a housing defining a fuelchamber, an all-speed centrifugal governor and coacting valve assemblymounted in said chamber including a sleeve provided with a valve port, ametering valve having said restriction, means responsive to an operatingcondition of the engine for controlling said regulator valve, means formaintaining a substantially 1 constant pressure drop across saidregulator valve and throttle valve, an engine driven variable a slidablemounting with respect to said sleeve and provided with one or moremetering orifices coaching with said port, a governor spring adjust?able to reset the governor, means for variably tensioning said spring toselect an operating speed for the engine, means accessible exteriorly ofthe housing for adjusting said sleeve with respect to said valve tofacilitate calibration of the device,- and means for maintaining ametering differedtial across said valve.

22. A fuel control device as claimed in claim 21 wherein there are meansaccessible exteriorly of said housing for adjusting the minimum enginespeed setting of said overnor independently of said spring tensioningmeans.

23. In a fuel control system for aircraft gas turbine engines, a fuelcontrol device having a fuel conduit provided with a meteringrestriction, a throttle valve for varying the effective area of saidrestriction, a pilots control member for resetting said valve, meansresponsive to changes in density of the air flowing to the engine forautomatically reducing fuel flow across said restriction as densitydecreases as by an increase of altitude, means for indicating to a pilota predetermined low fuel flow setting for said throttle valve, and analtitude idle flow orifice for conducting fuel to the engine when thethrottle valve is at its low fuel flow setting, the flow through saididle orifice being uncompensated for changes in entering air density tensure a minimum idle flow at high altitudes when the pilot throttlesback to a low or idle speed setting.

24. In a fuel control system for aircraft gas turbine engines, a fuelcontrol device having a fuel conduit provided with a meteringrestriction, a throttle valve'for varying the efiective area of saidrestriction, a pilots control member for resetting said valve, means forautomatically compensating the metering head across said restriction forchanges in density of the air flowing to the engine, means forindicating to apilot a predetermined low or idle speed setting for saidthrottle valve, an altitude idle flow orifice upstream of said meteringrestriction for conducting fuel to the engine when the pilot throttlesback to a low or idle speed setting, means for adjusting the area ofsaid restriction, flow through said orifice being uncompensated forchanges in air density.

WALTER L. DRAY.

FRANK V. KUZMITZ.

REFERENCES CITED The following references are of record in the file ofthis patent:

Number 22 UNITED STATES PATENTS Name Date Edwards May 12, 1931 BurgerOct. 12, 1937 Ifield et a1. July 2, 1946 Watson et a1. Oct. 5, 1948 10Number Chamberlin et a1. Aug. 23, 1949 FOREIGN PATENTS Country DateGermany Mar. 11, 1935

